/Engine/Source/Runtime/Core/Public/Misc/CoreDelegates.h
[iOS only] Called when the mute switch is detected as changed or when the volume changes. Parameter 1 is the mute switch state (true is muted, false is unmuted). Parameter 2 is the volume as an integer from 0 to 100.
static [TMulticastDelegate](API\Runtime\Core\Delegates\TMulticastDelegate)< void(bool, int)> AudioMuteDelegate;